He has become “increasingly lethargic” in recent weeks and medical staff believe he is ailing from a bacterial infection in his lungs, executives said on “SeaWorld Cares,” one of the company’s blogs.

“If Tilikum would have shown up with this disease in the wild, there’s no doubt in my mind he’d have been gone a long time ago,” SeaWorld veterinarian Dr. Scott Gearhart said in a video on Tilikum included in the blog post.

“I wish I could say I was tremendously optimistic about Tilikum and his future,” Gearhart said. “But he has a disease which is chronic and progressive and at some point might cause his death.”

The defunct Sealand of the Pacific in Canada captured Tilikum in 1983, and he moved to SeaWorld 23 years ago. A Sealand trainer who fell into a tank holding Tilikum and several other whales drowned in 1991, and a man was found dead on Tilikum’s back after apparently sneaking into his tank for an overnight swim in 1999, the Orlando Sentinel reported.

“Blackfish” blamed the psychological effect of SeaWorld captivity on Tilikum’s attack and drowning of Brancheau. The parent company’s gate receipts have fallen each year since the film was released in 2013 and it also faces multiple lawsuits, SeaWorld Entertainment’s latest annual report shows.

Company executives admitted last month they sent an employee to infiltrate the ranks of The People for the Ethical Treatment of Animals, which opposes the theme parks. PETA said on Twitter Tuesday that Tilikum should be allowed to “swim in the ocean one last time.”

“If Tilikum never sees the ocean again, after being stolen from it 30 years ago, his blood will be on #SeaWorld's hands,” PETA tweeted.

Yet Tilikum has fathered more than 20 calves during his time at SeaWorld, NPR reported. He and 28 other orcas live as part of “our family” at SeaWorld parks, where the care for the animals is accredited by The Association of Zoos and Aquariums and the Alliance of Marine Mammal Parks & Aquariums, according to the company.